This application is a continuation of prior application Ser. No. 12/126,740, filed May 23, 2008, entitled “EVALUATING A CLEANING SOLUTION USING UV ABSORBANCE”, by inventors Puri et al., from which priority under 35 U.S.C. §120 is claimed which is incorporated herein by reference in its entirety for all purposes
The present invention relates generally to cleaning solutions used in a wide variety of cleaning applications. More particularly, the present invention relates to evaluating the effectiveness of a sonicated cleaning solution used for cleaning substrates.
U.S. patent application Ser. No. 10/886,785, filed on Jul. 7, 2004, entitled “Systems and Methods for Charging a Cleaning Solution User for Cleaning Integrated Circuit Substrates” and U.S. patent application Ser. No. 11/093,904, filed on Mar. 29, 2005, entitled “Systems and Methods for Single Integrated Substrate Cleaning and Rinsing,” among other things, disclose cleaning IC substrates using a sonicated solution. The sonicated solution is produced by applying acoustic energy (e.g., megasonic energy) to a solution containing a solute. In a subsequent step, the sonicated solution is used to effectively clean the IC substrate.
The above-mentioned sonicated solution offers advantages that are not realized by the conventional cleaning solutions, which employ a concentrated ammonia hydroxide solution known as the Standard Cleaning Solution 1 (the “SC-1 solution”). In fact, cleaning using concentrated solutions suffers from several drawbacks that are not encountered when cleaning using sonicated solutions, which are extremely effective, under superdilute or near zero dilutions. Concentrated solutions run the risk of unduly etching, which appears as surface roughness and causes damage to the substrate surface and devices undergoing cleaning. In a non-patterned IC substrate, for example, over etching damages the real estate on the substrate surface, upon which circuitry and transistor devices are subsequently fabricated. For this reason, the resulting semiconductor chip may suffer from poor electrical performance or complete malfunction.
Dispensing highly concentrated cleaning solutions to drain poses environmental concerns. As a result, the concentrated effluent stream exiting the clean system requires appropriate treatment. The cost of an effluent treatment system and labor to implement the cleanup process make cleaning using the SC-1 solution expensive.
Concentrated cleaning solution also deposit on the surface undesirable metal contaminants which degrade device performance. Moreover, the peroxide composition of the cleaning solution typically contains stabilizers, which is another source of contamination that leads to performance issues. The problem is further exacerbated when relatively high composition of peroxide is used as part of the cleaning solution.
Of particular concern is cleaning integrated circuit (“IC”) substrates, including semiconductor substrates, that require removal of contaminant particles which adversely impact current circuit geometries. With the miniaturization of the circuitry on ICs, device sizes are currently approaching progressively smaller scales and such small devices densely populate the IC substrate surface. Contaminant particles of a certain size, which previously did not pose a threat to an IC's performance because the early generation of ICs were not as densely populated, now have a significant impact on the electrical performance of current ICs having miniature geometries. In fact, the contaminant particles can render the IC useless. As a result, an effective cleaning method for removing such contaminant particles, without damaging the substrate surface, is critical to enhancing the yield of ICs.
As a result, IC fabrication facilities are selecting the above-mentioned sonicated cleaning solution to replace the SC-1 cleaning solution, which has been the cleaning solution of choice for most in the semiconductor industry during the last forty years.
Unfortunately, currently there exists no objective method for evaluating the effectiveness of a sonicated cleaning solution in a cleaning process.
What is, therefore, needed is a method for evaluating the effectiveness of a sonicated cleaning solution in a cleaning process.